Biology and Peculiarities of the Population-genetic Structure of Lithuanian Cephalaspidomorphs (Cephalaspidomorphi)

Typically, studies of ichthyocenoses in Lithuania are being carried out to investigate the distribution, abundance and conservation status of bony fish communities. Cephalaspidomorphs as a group possess a distinctive life cycle. Therefore, researches into lampreys in Lithuania are fragmented and knowledge on species diversity, distribution, abundance and status of lamprey populations in Lithuania is poor. The present thesis reviews the distribution and abundance of Lampetra fluviatilis (Linnaeus, 1758) and Lampetra planeri (Bloch, 1784) in Lithuanian rivers, as well as the factors that affect dispersion and abundance of the larval stage of lampreys. By applying a molecular approach to identification of lamprey species, representatives of the Ukrainian lamprey Eudontomyzon mariae (Berg, 1931) were discovered inhabiting several rivers in Lithuania for the first time. A phylogenetic analysis based on mtDNA markers revealed that L. fluviatilis and L. planeri belong to the same evolutionary lineage. Additionally, the findings suggest that the Baltic Sea Lampetra spp. populations might experience the gene flow between two life strategies, which is supported by a successful in situ experimental hybridisation between L. fluviatilis and L. planeri spawning in communal redds. These findings are essential to the understanding of the population genetic structure of L. fluviatilis and L. planeri and contribute to the current knowledge of the speciation mechanism. From a practical point of view, the findings can be used in lamprey conservation. The current lamprey conservation status is assessed, and recommendations for further lamprey research and monitoring in Lithuania are given